Why are we reliant on an economist to pick up on this irrigation issue? You at least need people from industry to be consulted before regulations like this. Lucky that this particular person noticed the problem, but there probably shouldn't be a lawyer, a scientist and an economist making centralised farming regulations.
The typical cycle is that something obviously bad happens to an identifiable victim that can be traced to lack of regulation, then congress and/or the courts force regulation, and then the regulation causes a lot of invisible harm that may or may not be greater than the harm it prevents. My job is to try to make these inevitable regulations do more good than harm.
There would have been a public notice and comment period before the rule went final. But industry often fails to notice things, and quite often, when industry asks for standards to be lowered, consumer groups reflexively insist that they remain as proposed. The outcome ends up being based mainly on politics, which is why getting the proposal right matters.
It's naive to think that effective, efficient regulation can happen without consulting the people actually affected. It's also naive to think those people should be the ones making regulations.
Even beyond the inherent problem with industries regulating themselves, they are just not capable of doing so in many cases, especially farming. What does a farmer know about public health, or water-borne pathogens, or heavy metals? Farmers know what makes plants grow or not. They don't know how those plants affect the people that eat them.
Plus, says who that irrigating with drinkable water is even a bad idea? It's the most accessible standard. Drinking water is everywhere. It's literally the most unscientific reasoning possible that manure is dirty, therefor water can be dirty too. Self righteous, pretentious stories like this are everywhere, where the clever, down to earth common guy stumps all the big brains. The fact is that the people who study the effects of an industry are in a far better position to assess regulation.
Yes- a producer will be able to say that a regulation may be burdensome. They will definitely not be the best person to know if it's warranted or not.
However, if the water will go through manure before being absorbed by the the plant's roots, it is very wasteful to first purify it to drinking-water standard. Drinking-quality water is not everywhere in the quantities needed for irrigation, it requires expensive filtration and processing. Everyone saw the logic of this when it was pointed out, nobody was 'stumped'.
Or very useful --sometimes even demonstrably so (e.g. tragedy of the commons).
Centralized economic planning never works well, anyway, regardless of how many trained economists are at the helm.